Electro-optical dipolar material

ABSTRACT

An article of manufacture is provided as a matrix having dispersed substantially uniformly therethrough a plurality of electro-optically responsive dipole particles selected from the group consisting of electrically conductive and semi-conductive material and dichroic crystals, the matrix being a transparent medium capable of being in the fluid state during the initial orientation of the dipoles, whereby the dipoles are capable of rotation to a desired preferred orientation upon the application of a force field, the medium being thereafter solidified. A method of applying the force field is disclosed.

United States Patent Marks [54] ELECTRO-OPTICAL DIPOLAR MATERIAL [72]Inventor: Alvin M. Marks, 166-25 Ninth Avenue,

Whitestone, NY. 11357 [22] Filed: Feb. 16, 1970 [21] Appl.No.: 11,696

Related U.S. Application Data [63] Continuation-in-part of Ser. No.378,836, June 29,

1964, Pat. No. 3,512,876.

DIPOLE PARTICLES PARALLEL T0 sum-A E U/VPDLAR/ZED L/Gur ANDOM V/gRATIONS REFLECIED LIGHT POLAR/ZED NOIZIZONTALLY [451 Apr. 4, 19723,205,775 /1965 Marks ..350/147 X 3,350,982 11/1967 Marks.... ..350/152X 3,353,895 ll/1967 Emerson... ..350/147 X 3,443,854 5/1969 Weiss..350/147 3,536,373 10/1970 Bird et al. ..350/147 Primary Examiner-DavidSchonberg Assistant Examiner-Paul R. Miller Atlorney-Philip D. Amins[57] ABSTRACT An article of manufacture is provided as a matrix havingdispersed substantially uniformly therethrough a plurality ofelectro-optically responsive dipole particles selected from the groupconsisting of electrically conductive and semi-conductive material anddichroic crystals, the matrix being a transparent medium capable ofbeing in the fluid state during the initial orientation of the dipoles,whereby the dipoles are capable of rotation to a desired preferredorientation upon the application of a force field, the medium beingthereafter solidified. A method of applying the force field isdisclosed.

26 Claims, 13 Drawing Figures TEAL/SMITH?!) LIGHT IZE IV THEPOLARIZATION FFFECTY 0F DIPOLE 542 775255 OIPIENTEU /N 7' ll! PLANE of77/5 SURFACE.

PATENTEDAPR 41972 3,653,741

SHEET 1 OF 5 X DIRECTION OF ELECTRIC VECTUR OF LIGHT: POLARIZATION AMPLr005 pawns/Wad") &

A L ma VELENGTH (coma) THE THREE FUNDAMENTAL A RIB TE OF LIGHT ARE 2AMPLITUDE, WA VELENG'I'H, WAVELENGTH 4ND POLAR/Z4 T/ON FIG. I

POLAR GRAPH 0 RELATIVE RESPONSE VERSUS ANGLE OFA D/POLE 7'04 CONSTANTSIGN 4 INTENSI 7').

Q 11 35 Q cos u; [a l Y I 90 /ao ANGLE POLAR/ZA T/QN 0105c T/ONINVENTOR. DIPOLE ANTENNA 41 1 MARKS RElAT/VE Reva/vs: OFA DI OLE Awe-m4mesa: poue/zn r/o/v 0025c mu ;0. I

FIG. 3 ATI'DR/VE S PATENTED PR 4 m2 SHEET 2 OF 5 LIGHT HALF WAVE DI OLEWITH I. CENTRAL LOAD RESISTOR 2. DISTRIBUTED RESISTANCE SHOW/N6 HALF WAVE DIPOLE WITH CHARACfER/ST/C LOAD QES/STOR TUNED T0 ABSORB MAX/MUMPOWER.

FIG-4 PHYS/CA1. CR S 5 SECTION A floo A NA EFFEcr/ve A .50 cnosssear/01v n/cwsss A254 AZ/B suowlm mar rue EFFECTIVE c2055 SECTION OFAN 5ANTENNA MAYBE MANY 77,4155 ms PHYSICAL cm sear/01v,- uv 77115 case msx.POWER IS fwwveusa FROM mv EFFECflV' c1205: SECTION mm ms SMALLER ACTLMLcross SECTION or THE ANTENNAE.

A woven/mm INVENTOR J41 w/v M. MARKS A rron/vsrs s/mwnva ms RELA m1:POWE'R nesoeaso on RRAOMTD vexzsu:

mamas/var Fae m/cK A/VD EKJENTED R 1 72 3,653,741

SHEET 3 0F 5 DIPOLES NORMAL SUI/"A C E 7 PARTICLES AL/GIVED NORMAL TOTHE SURFACE COAT/N6 l5 TRANSPARENT.

TBMIQVITTEO L/GH T DIPDL E POLAR/ZED PARTICLES YER T/CALL Y PAMLLEL T0SURFA CE UNPOLA RIZED Ll GUT RANDOM V/BRA TIONS REFLECTED LIGHTFULAR/ZED HORlZ0/VTALLY 8 syows THE POLARIZATION EFFECTS OF DIPOLEMRWCZES ORIENTED IN 77/: PLANE OF THE SURFACE.

DIPOL E 5 WI T H RANDOM DIRECT/0N mow M6 DPO s HAVING .4 xzwvao/wINVENTOR- FIG. 9 4 5442 PXJENTED 4 1973 SHEET [1F 5 INCIDENT LIGHTfiuwwm) PULSE Y APPL IED EL EC TR/C Z w. m P

FIELD FLU/O O12 PLASTIC LAYER WHICH HAROE'NS SUPPORT 01 ARIZEDZANSMITTED RAY AZUMINUM FLARE POLAR/ZED FIGBA INVENTOR. AL WM 1% MAQKSThis application is a continuation-in-part of U.S. application Ser. No.378,836, filed June 29, 1964, in the name ofAlvin M. Marks, now U.S.Pat. No. 3,572,876.

This invention relates to conducting dipole polarizers and articles,products, devices, and the like, produced therefrom having preferredoptical properties, the conducting dipoles being advantageously formedof metals, non-metals, or semiconductive materials capable of formingwhiskers by vapor deposition or capable of forming submicron rod-likeshapes by using metallurgical melting and controlled freezingtechniques, growth from a vapor, or other known techniques. The dipolesare suspended in a transparent layer of material capable of beingcongealed or hardened after the dipoles have been oriented in thedesired direction.

RELATED APPLICATION In related application Ser. No. 378,836, now U.S.Pat. No. 3,512,876 methods and apparatus are disclosed for controllinglight and related forms of electromagnetic radiation using dipoleparticles suspension in transparent media. By employing an externalelectrical or magnetic field, the optical properties of the media can bevaried by orienting and disorienting the dipolar particles in suspensionin accordance with the field applied, the media being a fluid in whichBrownian movement aids in randomizing the dipole particles upon removalof the external field. In its broad aspects, the related applicationprovides a light-controlling device comprising in combination a fluidsuspending medium and a plurality of minute dipole particles rotatablycarried in the medium, the particles advantageously having a longdimension of the order of about )t/2n and at least one other dimensionpreferably not exceeding about 1 n (where A is the wavelength of lightand n is the index of refraction of the suspending medium). Thedisposition of the particles in the medium is controlled by applying anelectric, magnetic or mechanical shear force field to the suspension.One example of a light-controlling device is an electro-optical shutter.The related application goes into great detail in the technical aspectsof dipole particles, which disclosure is wholly incorporated into thisapplication by reference.

BACKGROUND OF THE INVENTION In the prior art, it is known to producemetal polarizers by the reduction of metal salts in stretched polymers,such as cellulose hydrate, gelatin, polyvinyl alcohol, and the like. Themetals so reduced form aggregates within the interstices of the polymer.Such aggregates are usually relatively uncontrolled as to length anddiameter. Since most polymers have disordered regions, irregularlyshaped metal deposits were often formed which detracted from thetransmittance and polarization characteristics. The polymers employed,were capable of swelling or dissolving in water, and were generallysensitive to ambient atmospheric conditions.

Elongated silver particles having a maximum ratio of three to one in theform of ellipsoid of silver, have been produced in glass by strongstretching. For a given mass per unit area of absorbent material, theabsorption obtained by such particles is greater than that of anordinary colorant, such as cobalt dissolved in the glass, by a factor ofabout 3,000 to one.

The prior art methods of stretching to deform particles do not enablecontrol of particle ratio of length/width, nor do they result in optimumlength/width ratios required for strong polarization.

Another polarizer described in the prior art consists of minute wires orconductors on a glass surface or within a glass structure. However, nopractical means for the production of such structures have beendisclosed. Very long thin conductors are not as efficient for producinga high degree of polarization and transmittance in a specific wavelengthrange. The dipoles herein disclosed may be fabricated by incorporationinto a suitable stable polymer or a glass melt and aligned by mechanicalshear forces, or an electric or magnetic field. It

would be desirable to have a dipole particle which is inert and whichwill resist degradation during use in the ambient environment.

OBJECTS OF THE INVENTION It is an object of the invention to provideconductive and semi-conductive dipole particles which are substantiallyinert to the ambient environment and which resist degradation.

Another object is to provide as an article of manufacture a transparentmaterial, such as a solid material made of glass or transparent plastic,characterized by a dispersion of microscopic, inert, dipole particlesoriented to confer light polarizing properties on the material.

A further object is to provide a solid transparent substrate having atransparent coating thereon containing a dispersion of submicron, inert,conductive, dipole particles having a preferred orientation, whereby toprovide predetermined optical properties to the coated substrate.

A still further object is to provide a composition of matter for opticaluse, said composition comprising a suspending medium containing aplurality of dipole particles, the medium being one capable of beingconverted to the fluid or soft state to enable orientation of theparticles and capable of being solidified to permanently fix theposition of oriented dipole particles.

The invention also provides as an object a method of producing dipoleparticles of relatively controlled sizes.

These and other objects will more clearly appear when taken inconjunction with the disclosure and with the accompanying figures of thedrawing which are summarized as follows:

IN THE DRAWING FIG. 1 illustrates the three fundamental attributes oflight;

FIG. 2 is a polar graph showing relative response versus the angle of adipole to a constant signal intensity;

FIG. 3 shows the relative response of a dipole antenna versuspolarization direction;

FIG. 4 depicts a half-wave dipole with a characteristic load resistortuned to absorb maximum power;

FIG. 5 illustrates diagrammatically the effective cross section of adipole antenna as compared to the actual physical cross section;

FIG. 6 is a graph showing the relative power absorbed or reradiated as afunction of the wavelength of light for thick and thin half-wavedipoles;

FIG. 7 depicts a transparent substrate, e.g. glass or plastic, having atransparent coating, e.g. of plastic, in which dipoles are dispersed andoriented normal to the surface of the coat- FIG. 8 is similar to FIG. 7except that the dipole particles are oriented parallel to the surface toprovide polarization effects, whether the coated article is a lens, acoated windshield for automobiles, coated sheet material, and so forth;and FIG. 8A shows flake orientation;

FIG. 9 is similar to FIGS. 7 and 8 except that the dipoles in thecoating are randomly oriented;

FIG. 10 is a diagrammatic cross sectional view of a machine for thecontinuous production of polarizing film or sheet utilizing dipoleswhich are electrically aligned;

FIG. 11 is a detailed fragment of the electrical aligning section of thedevice of FIG. 10; and

FIG. 12 is a vertical cross section of a high pressure spin coatingdevice for producing high field orientation dipole suspension coatings.

GENERAL STATEMENT OF THE INVENTION The present invention overcomes thedeficiencies of the prior art by providing metal whisker dipoles orsubmicron rodlike dipoles of relatively inert material such as chromium,aluminum nickelide, platinum or other conducting metal; oralternatively, by utilizing semi-conductors which are advantageous forcertain other characteristics, such as silicon, germanium, or zincsulfide whiskers, and having a selected length, and length to widthranges.

These are preferentially incorporated in a readily meltable glass,thermoplastic or plastic solution, and orientated by means well known tothe art, such as by the application of an electrical or magnetic fieldor by the application of stretching where differential shear is producedduring stretch causing the parallel orientation of the particles, andsubsequently solidified by cooling or evaporation of solvent.

Thus, as one broad aspect of the invention, a composition of matter isprovided for optical use comprising a plurality of conductive orsemi-conductive asymmetric particles (e.g. dipoles) suspended in atransparent medium which is substantially a solid at ambienttemperatures but which can be melted or softened to a fluid state at anelevated temperature to form any desired shape, the particles being thenoriented to a preferred direction by an electrical or magnetic fieldbefore allowing the shaped body to solidify.

Another aspect of the invention resides in an article of manufacture inthe form of a polarizer comprising a layer of transparent materialhaving a dispersion of inert conductive or semi-conductive dipoleparticles therein having a length of A/Zn i 50 percent, and preferablyhaving an average diameter of at least about IOn, where n equals theindex of refraction of the transparent medium, the long axis ofparticles being oriented in the plane of the transparent medium.

The dipole particles can be produced by various methods. Thus, metaldipoles can be produced by vapor deposition in a partial vacuum toproduce metal whiskers which can be sized in a blender and the sizesseparated by centrifuging or by differential settling.

Another method is to produce a eutectic of a binary alloy which, bydirectional freezing, produces a rod-like structure, the size of therod-like structure being determined by the velocity of the plane ofsoldification and temperature gradient. After selectively dissolvingaway the matrix metal, the residue of rod-like material is washed andthen suspended in an inert liquid for sizing in a blender, the sizedmaterial being thereafter selectively separated using differentialsettling or centrifuging techniques. The foregoing and other methodswill be described in more detail hereinafter.

The dipole particles useful in the present invention are characterizedin that they have at least one dimension large relative to at least oneother dimension, that is to say, they are in the form of flakes, needlesor the like. The dipole particles should haveat least one dimensionequal to one-half of the wavelength of the radiation to be controlled,(normally, visible light, but in some cases, infrared, ultraviolet,microwave, or other portions of the electro-magnetic spectrum) and atleast one other dimension substantially smaller than one-half of saidwavelength. The magnitude of the third dimension, that is, whether theparticle is a needle or a flake, depends on the requirements of thespecific embodiment of the invention, as more fully discussed below.

For purposes of brevity, the term light is used throughout the presentspecification and claims in a generic sense and is intended to encompassnot only visible light but also infrared and ultraviolet light, as wellas microwave radiation in the neighboring portions of theelectromagnetic spectrum.

In addition to the dimensional requirements herein disclosed, theelectrical or magnetic properties of the dipolar particles, i.e. theconductivity, should be such as to facilitate orientation in an electricor magnetic field, and strong interaction with electromagneticradiation.

The suspending medium is a fluid, non-reactive with the dipoleparticles, or is a substance capable of being converted to a fluid, at atemperature sufficiently low to avoid any adverse effect on the dipoleparticles.

It is not in all cases necessary that the suspending medium be in theliquid state during the first stage of orienting the particles.Providing the applied torque is sufiiciently strong to orient the dipoleparticles against a certain amount of plastic resistance of thesuspending medium, it is sufficient if the suspending medium is in ahighly deformable plastic state. The term fluid" as used herein shouldtherefore be understood to encompass such a plastic or soft condition.For most applications of the present invention, the suspending medium ispresent as a liquid during alignment or disorientation of the dipoleparticles. The dipole particles must also be of such a nature that theyare capable of being oriented by an applied electric, magnetic or, incertain cases, a mechanical shear force field.

Some particles have an inherent dipole moment by reason of theirinternal structure in which the effective center of positive charge inthe molecule or crystal is spaced from the center of positive charge.Such an inherent dipolar character, if present, is effective to somedegree in augmenting the tendency of the particles to orient themselvesin an applied force field. Inherent dipolarity is, however, neitheressential nor a major factor in determining the effectiveness of thedipole particles.

As stated hereinbefore, the preferred dimensions of the particles abovereferred to may be characterized by A/2n where A is the wavelength ofthe light to be polarized and n is the index of refraction of the mediumin which the particles are suspended and oriented.

For example, if a suspension of dipole particles is to polarize light at5,600A, and the index of refraction of the transparent suspending mediumis 1.5, the optimum length for the dipole whisker is 5,600/2 1.5=(5600/3) 1,860A. The length to diameter ratio should be not less thanthree, and preferably greater; that is, from 10 to 100. The percentageof polarization increases with the length/width ratio, and the width ofabsorption or reflectance band decreases. Where dipole particles arehighly conducting, such as with silver, gold or copper whiskers, thepolarizer acts as a beam splitter, and the radiation is partlytransmitted and partly reflected. The transmitted radiation is polarizedwith good image resolution. The reflected radiation, however, isscattered, and polarized in a plane at to that of the plane ofpolarization of the transmitted light.

A beam splitting polarizer of this type is particularly useful wherepolarization of intense light beam sources is required. In the case ofthe absorption polarizer, the temperature of the polarizing elementrises perhaps to cause destruction. However, with the beam splittingpolarizer, the radiation is mostly reflected and transmitted, and thetemperature rise is minimized.

The most efficient sheet polarizer is that which requires the smallestnumber of particles per unit area to accomplish a given percentpolarization. The most efficient sheet polarizer is obtained byselecting particles within a narrow size range, about the optimum A/Zndimension. For example, for most efficient polarization in the rangefrom 4,500A to 6,600A, dipole particles having length ranges between1,500A to 2,200A, are selected. For a still narrower range of polarizingcharacteristics, then a still narrower range of dipole particle lengthsis employed. For example, for a narrow frequency band which mightcharacterize a laser, then a single length with close tolerances isemployed.

Stable chemical structures are relatively rare. Most chemical structuresare relatively easily deteriorated by ultraviolet, visible and infraredlight, heat and chemical action.

Light is an electromagnetic wave having three fundamental attributes,which are: amplitude or intensity, wavelength or color; and polarizationor the vibration direction at right angles to the ray.

These three fundamental attributes of light are shown in FIG. 1.

A half-wave dipole antenna, which is normally used for televisionreception, has interesting properties.

The half-wave dipole is capable of controlling all three attributes oflight, by varying its length, thickness, resistivity and angularposition.

The electric power absorbed from the radiation by the halfwave dipoledepends upon two orientation angles of the dipole. The first angle, 6,is that between the length of the dipole and the signal path. The secondangle, 45, is that between the length of the dipole and the direction ofpolarization of the signal.

FIG. 2 shows a polar graph of radiant power absorbed versus angle 0.

In FIG. 3, the radiation ray path is normal to the plane of the diagram,and there is shown the angle versus the power absorbed by the dipole.

A maximum response is obtained when the antenna is aligned parallel tothe polarized electric vector of the radiation and at right angles tothe signal path ((12 0, and 90). The antenna absorbs no power when it isplaced at right angles to the polarized electric vector of theradiation; or arranged parallel to the ray path.

When adjusted for a maximum response, a half-wave or M2 antenna is thensaid to become resonant to the particular wavelength A.

The power absorbed by the dipole from the radiant energy may bere-radiated, or absorbed and dissipated as heat, depending on theelectrical resistance of the half-wave dipole antenna.

lf power is to be absorbed from the dipole antenna and utilized in anoutside electric circuit, as for example in a television set, a matchedor characteristic resistance of 73 ohms must be inserted at its centerof the half-wave dipole antenna, as shown in FIG. 4.

An antenna may be made of such material, thickness and length as toachieve full power absorption, or nearly total reflection.

In FIG. 4, there is also shown a half-wave (M2) antenna 2; in which thecentral resistor is replaced with a single rod having a distributedresistance of approximately 80 ohms, which results in the absorption ofradiation in the wavelength range it.

Now, if instead of a half-wave antenna with a central resistor or anequivalent distributed resistance, a half-wave antenna of low resistanceis employed, then the half-wave dipole antenna becomes reflective forthe full wavelength. The radiant power may be said to be absorbed by thehalf-wave dipole and then re-radiated in all directions, with theintensity direction pattern shown in FIG. 2. Thus, the resistivitycharacteristics of the materials, together with the length and width,controls the distributed resistance of the half-wave antenna. Thesefactors may be adjusted so that the half-wave dipole antenna has highabsorptivity or high reflectivity for incident radiation of a givenwavelength band.

FIG. 5 shows another very important property of the halfwave dipoleantenna, the effective cross section.

FIG. 5 shows a half-wave dipole antenna having a thickness of onetwenty-fifth its length. Its length is M2 and its thickness M50. Thephysical cross section of this half-wave dipole at right angles to thelight ray is:

()\/2) (M50) A /IOO. However, it is known that the effective crosssection of a half-Wave dipole antenna is much larger. The cross sectionfrom which the half-wave dipole appears to absorb power is approximatelyA /8. A rectangle of this size is shown in dotted lines surrounding theantenna rod, the radiant power actually funnelling into the dipole. Inthis example, the effective area of the antenna has been increased by afactor of A /B divided by XVIOO or 12.5 times.

Dipole antennas have been employed for the electro-magnetic spectrum allthe way from long wave radio down through the television range into themicrowave and millimeter wave spectrum.

Dipoles have been observed which are resonant in the range of thewavelength of visible light. Yellow light at the peak sensitivity of thehuman eye has a wavelength of 0.565 microns (yellow). Elongated metalrods of submicron dimensions in colloidal suspension in a transparentmedium, results in myriads of light-responsive dipoles. The transparentmedium keeps the dipoles in spaced relation.

The index of refraction n of a given medium may be defined as the ratioof the speed of light in free space, to the speedof light in the medium.Since the speed of light in all substances is less than in free space, nis always greater than one. The wavelength of light in a given medium isinversely proportional to the index of refraction n" ofthe medium.

Because the index of refraction of transparent media is approximately1.5, the dimensions of a half-wave dipole must be decreased in inverseproportion; that is, for n 1.5, the actual resonant length of ahalf-wave dipole in such a medium becomes r) A/l .5 =A/3.

For example, in a medium having an index of refraction of 1.5, ahalf-wave dipole should have a length of (0.565/3) 0.188 microns (or1880A) of yellow light for 0.565 microns wavelength (or 5650A).

The M3 dimension, of course, is correct only for n 1.5 and will varywith the index of refraction of the medium.

Another interesting property of the dipole is that the sharpness of itstuning, or the wavelength range over which it will absorb 0r reflect,depends on the ratio of the length to the thickness of the dipole, aswell as on the resistivity of the dipole material.

FIG. 6 refers to the reflection or absorption of radiant energy by ahalf-wave antenna showing the relative power absorbed or re-radiated,versus the ratio of length to thickness of the antennae.

A. For thin dipole antenna (25/1) B. For a thick dipole antenna (10/ ll)We now come to the application of these basic concepts to light control;that is, control of all three basic attributes of light, intensity,color and polarization, by dipoles in suspensions in a transparentmedium.

Pigments formed from dipolar materials are visually indestructable. Thepolarization, reflectivity or absorptivity characteristics of the dipolesuspensions are predetermined by the appropriate selection of length,width and resistivity of the dipoles, together with their concentrationand orientation.

Such a dipole suspension has the property of absorbing or reflectingspecified wavelength ranges. Since a specific resonance characteristicis obtainable from the same material merely by changing its length towidth ratio, very pure colors can be obtained by transmission orreflection from coatings formed from such suspensions. When oriented,the dipole suspension has strong polarizing properties.

The substances chosen to form the dipoles are preferably chemicallystable materials, which remain permanently within the suspension, andwhich are not subject to chemical destruction by ordinary atmosphericagents or by exposure to light. However, dichroic crystalline needles,such as herapathite dipoles, may be employed as dipoles.

The dipoles may be formed of metals, such as gold, platinum, palladium,chromium, tin, or metal compounds such as Al Ni, and the like, which areknown to grow submicron crystal-whiskers, under appropriate conditions,such as from the vapor phase. Semi-metals, such as carbon, silicon andgermanium, are also known to form crystal-whiskers. Thesecrystal-whiskers may then be incorporated in a fluid to form a dipolesuspension.

A crystal-whisker made of a single substance of the utmost permanence,may be predetermined in its properties; a perfect black, a perfect whitediffuse reflector, or having sharp absorptivity or reflectivity bands inthe yellow, green, blue or other regions of the spectrum. When oriented,these result in polarizing these characteristics.

The effective cross section per particle oriented normal to the lightray and parallel to the electric vector of the light in a I medium ofindex of refraction n is:

/8n (I) This property is useful in calculating the number of particlesrequired for substantially complete light absorption or reflection asfollows:

Assuming no aggregation of particles, the concentration of a suspensionof submicron dipolar particles per square centimeter in a medium havingan index of refraction of 1.5 is determined as follows:

= 6.25 X 10 particles/cm? It is possible to obtain the interparticlespacing between dipoles oriented in the same direction, theinterparticle spacing for substantially parallel dipoles being thecenter to center distance between the longitudinal axis of the particlestaken-at right angles to each other. The interparticle spacing forsubstantially complete light absorption or reflection does notsubstantially exceed the width of the effective cross section.

The derivation of the interparticle spacing, d,,, for the polarizingcase is determined where the dipoles are all parallel and disposed inthe plane of the sheet. The details are disclosed in copendingapplication (Ser. No. 378,836, filed June 29, 1964, and need not berepeated here. Simply stated, the interparticle spacing may bedetermined as follows:

N, the number of diples per unit volume of suspension V, volume of cubeoccupied by one dipole l/N,

d,,= interparticle spacing= V,,= l/N, 3

The concentration of dipole particles required to provide effectivesurface coverage is generally very low as will be apparent from thefollowing:

Assuming a square cross section for the particle having a width a, themass per particle is b= width to length ratio and 8= density in gms./cm.of the dipole.

Thus, the mass m, per dipole particle of gold for length to width ratioof 25 where 8 of gold equals 19 and b 1/25 is:

m, of gold 2 X l0 gms./particle.

The mass m, of dipoles per unit area is then determined as follows:

Thus, (it/n) b (particles/cm?) X (mass/particle) 6.25 x x 2 x 10- x 1.25x 10- gms./cm.

As will be noted, very small concentrations of dipole particles of theorder of about 2 micrograms/cm. are sufficient to provide effectivesurface coverage.

For a film of 10" cm.(0.4 mil) thickness, and density l gm./cm. thiscorresponds to a dipole concentration of only 0.125 percent of the solidfilm.

Because their effective cross section is much greater than the physicalcross section, the dipolar particles may be very sparsely distributed inspace. The dipolar particles are sufficiently far apart from each otherso as to have no physical interaction. Each dipolar particle actsindependently of the other.

FIG. 7 shows a film containing dipole particles with their lengthoriented normal to the surface. The film is transparent because thecross section particles present to the radiation is so small thatsubstantially no light scatter and no light absorption occurs.

FIG. 8 shows a film in the XY plane in which the dipole particles arealigned in the OX direction. Light transmitted along the Z axis into thesurface emerges from the other side plane polarized with the electricvector By in the ZY plane. Reflected light is plane polarized with theelectric vector E I in the ZX plane. Reflected light is polarized andscattered.

FIG. 9 shows a film having dipolar particles in random orientation.Reflected light is symmetrically scattered in all directions. Thetransmitted light and the reflected light show no polarization. However,since the dipoles are tuned to a particular wave band, the transmittedand reflected rays are complementary in color. Consequently, in therandom orientation, the dipoles act as pigments. However, these dipolarpigments are subject to control by variation of physical quantities ofdimension resistivity and orientation.

As stated hereinabove, dipoles may be oriented by an electric field, amagnetic field (if the particle is magnetic, diamagnetic orparamagnetic), or by viscous shear forces in the suspending fluid.Dipole particles tend to disorient rapidly in suspending fluids of lowviscosity. For low viscosity fluids obtained by heating to a fluidtemperature, the disorientation of dipolar particles may occur inmilliseconds. The disorientation is due to Brownian movement or therandom impact of the fluid molecules on the dipole particle.

However, if the suspending fluid viscosity is high, dipole orientationwill persist for a longer time, from seconds to hours. A permanentorientation of dipolar particles may be achieved in a fluid by allowingthe solvent, in the case of a plastic composition, to evaporate whilemaintaining the orientation.

Metallurgical techniques may be employed to produce dipoles. A knowneutectic method for the manufacture of metal dipoles has producedchromium rods and aluminum nickelide rods having a length/width ratio ofabout 100, in a range of diameters from 50A to 300A, and lengths toabout 40,000A. The method involves the precipitation of one metaldissolved in another; for example, chromium precipitated from achromium-copper melt, using a travelling temperature difierential, ordirectional cooling from one end of a melt. The solidification rate mayvary from about 0.1 to 10 cm./sec. at a temperature gradient of about 1to C./cm. Subsequently, the copper is dissolved in acid, leaving longthin chromium metal rods having a submicron diameter, and of variouslengths. After the extraction of the metal rods, they can be furtherdecreased in size using acid of controlled concentration. Thus, wherethe diameter is 500 to 1,000A, acid treatment can further decrease thediameter.

It has been found that long rods may be chopped into shorter lengths ina suitable range by the following procedure. The metal rods aresuspended in an inert fluid. The fluid may comprise water, alcohol, oran ester with or without dissolved polymer. The polymer helps to suspendthese particles. The suspension is placed in a high speed blender, therevolving metal blades of which cause strong shear and impact forces tooccur. Most of the cut rods do not appear to be bent but appear to becleanly sheared into shorter straight rods.

It is theorized that the particles are cut by high speed impact orpossibly torn asunder by opposing turbulent shear forces. Whatever thephysical explanation may be, the rod lengths varying from about 700A upto the maximum particle length are placed in suspension. The particlesare then separated into size ranges by fractional centrifugation or byelectrophoresis. The larger particles, in the case of centrifugation,are thrown down as the first centrifugate and then successively smallerranges of particles are thrown down into the centrifugate. Finally,there remains only smaller particles of irregular shape of a very smalllength/width ratio. A suitable intermediate ratio range is selected andthe process may be repeated, using a smaller viscosity fluid ifrequired, to get a narrower range of ratios. These particles are thenfiltered and washed with solvent and vacuum dried.

Where glass is used as the final matrix, the selected dipole rods arethen mixed with finely powdered glass frits, of a suitable compositionwell known in the art. This mix is melted, stirred, debubbled, and castto form sheets. These sheets, when heated to a high viscosity, may bedrawn by stretching to orient the dipolar particles. Alternatively, thesheets may be melted or softened at high temperatures to a lowviscosity, and the dipole rods oriented by electrical means. To producea light polarizing sheet, the orientation is carried out to position thedipoles parallel to the surface.

To produce a uniaxial polarizer of the type described in my US. Pats.Nos. 3,205,775 and 3,350,982, the dipole rods are oriented normal to thesurface of the sheet. To obtain a wedge-shaped transmission patternrequires a combination of two sheets in which the dipole rods areoriented respectively parallel to, and normal to the surface; that is, acombination of uniaxial and linear polarizing sheets.

Various techniques known in the art of glass making may be employed. Forexample, continuous drawing methods may be employed using a glass meltcontaining dipoles, and the drawing and rolling of the glass will causethe orientation of the dipolar particles to produce polarized glass.Various selected size ranges may be employed to produce sharp absorptionand reflection bands.

To polarize the entire visible spectrum, selected length ranges ofdipole rods varying in length from about 1,000A to 2,500A may beemployed. To produce glasses which will polarize the infrared, largerparticles are employed from about 2,100A up to about 10,000A in lengthto polarize infrared in the range of l to 30 microns. Thus, broadlyspeaking, the length of the dipoles may range from 1,000A to 10,000A,the ultimate size being determined by the particular end use.

Polarizers may also be made by incorporating these dipolar rods in thesame selected size ranges in polymers normally employed for polarizingmaterials; ie polyvinyl alcohol, polyvinyl butyral, and these subjectedto mechanical elongation to orient the particles in a manner well knownin the art.

Another method which may be employed advantageously is the incorporationof the particles in a polymer solution, such as a silicone polymersolution, which has a high degree of stability at an elevatedtemperature. This solution may be employed by flowing or spinning acoating onto a glass surface, for example, a lens, which is subjected toan electrical field just before it dries, while the dipoles are free toturn. The di ole rods may be oriented with their long axes parallel tothe surface by applying an electrical field parallel to the surface orthe dipoles may be oriented normal to the surface by the application ofan electrical field normal to the surface.

The polymeric coating containing the dipoles is set by allowing thefluid to evaporate. The dipoles may be placed in a monomer and orientedby electrical fields while the monomer is setting. Alternatively, themonomer may be stretched when partially polymerized to orient theparticles by mechanical shear forces and then finally set by completingthe curing process.

As illustrative of the various methods which may be employed inproducing conductive dipoles, the following examples are given:

EXAMPLE 1 Flake Dipole Suspensions To prepare metallic flakes for use asdipole particles, a layer of metal is deposited, for example, by knownvacuum deposition techniques, on a film of plastic or other convenientsubstrate, and the substrate is subsequently dissolved, thus causing themetal film to be suspended as a flake in the solvent. The suspended filmis then chopped to flakes of the desired size by using a Waring blenderand the desired sizes separated by differential centrifugation.

EXAMPLE 2 Ultrathin Aluminum Flake Suspensions A novel method ofpreparing ultrathin aluminum flake suspensions uses aluminum flakes 1-17microns in diameter, and 0.1 to 1 micron in thickness as the startingpoint. A suspension is prepared by adding 48 grams of the aluminum flakematerial to 300 cubic centimeters of di-isooctyl adipate. This mixtureis then shaken and poured into a 500 cubic centimeter graduated cylinderand allowed to settle. Most of the aluminum flakes then settle to thebottom of the graduate. However, a small portion of the flakes remainssuspended in a thin layer at the top of the graduate. This top layerthen comprises ultrathin aluminum flakes, approximately 0.1 micron inthickness, which are then recovered.

Thus, by means of this flotation method, the 0.1 micron thickness flakesare separated from the thicker flakes. These ultrathin flakes may befurther separated and concentrated by centrifuging.

Another way to make thin flakes of aluminum or the like is to coat athin rubber sheet with a film of aluminum by exposing it to aluminumvapor, until a film of approximately 0.01

l fl micron thickness has been built up. This sheet is then stretched tobreak up the surface into flakes of aluminum. The underlying rubbersheet is next dissolved in order to place the flakes in suspension.Finally, the large flakes are eliminated, and the small flakes in thedesired size range are concentrated, by centrifugation. This techniquecan also be employed using polyvinyl alcohol or polyvinyl chloridesheets by heating the sheets after the coating step, to facilitate theirbeing stretched.

The resulting suspension is suited for use in those embodiments of theinvention which require a suspension of dipoles in the form of flakes,for example, the Reflective-Absorptive devices, discussed in thereferenced copending application.

XAMPLE 3 Needle-like Metal Dipole Suspensions diameter in the submicronrange, and deposit a film of aluminum on the thread by passing thethread through a zone or chamber in which it is exposed to aluminumvapor. The thread is then wound on a spool, and sliced with a microtome.Finally, the supporting thread is dissolved in a suitable solvent,

leaving the metal coating in the form of thin aluminum strips incolloidal suspension.

EXAMPLE 4 Needle-like Metal Dipoles from Whiskers Needle-shaped metallicdipoles may be formed from a metal, such as gold, platinum, palladium,chromium, tin or the like, which are known to grow submicron-diametercrystal whiskers under appropriate conditions, usually from the vaporphase. These crystal whiskers may then be incorporated into fluid toform a dipole suspension. Such needles, if classified to a uniformlength, may be made sharply selective as to the wavelengths of lightaffected by them. This property results from their largelength-to-thickness ratio and resistivity, for reasons which areexplained below. Such materials constitute a new class of pigmentsdifferent in effectiveness and mode of operation from conventionalpigments.

The factors controlling the growth of needle-like whisker dipoles arepartial pressure and temperature of the metal vapor, temperature andnature of the deposition surface, and time of growth. Usually, thegrowth occurs best under vacuum, or inert gas such as helium ornitrogen, but, in some cases, as with gold, whiskers can be grown inair. Two gold sheets separated by a few millimeters and by a few degreestemperature difference, held in air at a temperature such as to generatean appreciable gold partial vapor pressure, will cause gold whiskercrystals to grow normal to the surface of the cooler gold sheet. Thedimensions of the whiskers are such as to fall within the size rangesherein specified. On cooling, the whiskers may be incorporated in aplastic film formed by coat ing the surface of the gold sheet,encompassing the whiskers. Upon drying, the film may be stripped awayand dissolved, leaving the gold dipoles in suspension in the fluid. Thisprocess may be performed continuously using an endless belt of amaterial, such as stainless steel, which is initially provided withactive sites for initiation of whisker growth.

Flat Crystals Flakes made from crystalline material, such as leadcarbonate (pearlescence), may be grown to any desired size by methodswell known to the art. These flakes have an index of refraction of about2.4, and, when placed in a fluid having an index of refraction of about1.5, are readily aligned by an electric field, and in the equivalent ofabout -20 layers almost totally reflect visible ultraviolet and nearinfrared radiation, when disoriented or oriented in the plane of thecell wall or sheet; while being almost completely transparent whenaligned normal to the sheet surface.

Zinc vapor will deposit submicron flat crystals on a substrate, whichcan be dissolved away as above described, to yield a metal flakesuspension having dipolar characteristics.

Graphite forms flat hexagon flakes which, when suspended in a fluid oflow viscosity, show dipolar characteristics.

EXAMPLE 6 Metal Coated Preformed Dipoles Preformed rods of Boehmite(colloidal alumina) are metalcoated by vapor deposition. The Boehmite isin the form of minute crystalline rods or fibrils having a length ofapproximately 1,000A and a width of about 5A. In metal coating thefibrils, the Boehmite crystal rods are heated to various elevatedtemperatures while exposed to the metal vapor.

Another method is to coat Boehmite particles by chemical deposition. Forexample, Boehmite particles may be soaked in a solution of a metalhalide or nitrate, such as gold chloride, gold nitrate or silvernitrate. The particles are washed to remove all but the adsorbed salt.The Boehmite powder is then heated to a temperature of about 300 C todecompose the adsorbed salt and thus produce a coating of silver or goldmetal on the Boehmite.

EXAMPLE 7 Production of Dipoles from Binary Eutectics Metal fibers canbe prepared by the unidirectional solidification of binary eutecticalloy. A well known example is the system Al-Al Ni. The alloy containingabout 5.7 percent to 6.4 percent by weight of nickel and the balancealuminum is produced by melting together high purity aluminum (99.99percent) and high purity nickel (99.99 percent). The melts areunidirectionally solidified using induction and resistance heatingsources by maintaining a thermal gradient during cooling. Whiskers orrods of Al Ni are formed lying parallel to each other in the directionof solidification and dispersed through an aluminum matrix. Byincreasing the rate of cooling, the diameter of the needles or rods canbe increased. The Al Ni whiskers may be extracted from the aluminummatrix by using a 3 percent solution of aqueous HCl solution. As soon asthe whiskers are dislodged, they are removed rapidly from solution andare washed. The whiskers can be graded according to size by differentialsettling or differential centrifugation as described hereinbefore. Splatcooling may be employed by striking metal droplets against a coldsurface of high heat conductivity.

Examples of other eutectic alloys are the following:

Au-Ca Au'13.2% Ca Ca Au. Au Au-Na Au-17% Na NaAu, Au Au-Sb Au-347c SbAuSb, Au-0.64% Sb Au-Te Te-47"7 Au AuTe Au Au-Tl fl-27.7% Au T1 Au Au-UAu-12.5% U U Au, Au

' Atomic percent As will be noted, the fibers contain substantially onemetal, that is, some of the compositions yield fibers which at worstcontain less than 1 percent of the second metal. Of the 13 systemslisted, five may yield fibers of pure or nearly pure metal in a matrixof a second pure metal, such as Ag-Bi, Ag- Pb, Al-Ga, Al-Sn and Au-Tl.There are other systems, among which is included the system Cu-Cr.

The resistivities of some of the metals are given as follows:

TABLE 2 Resistivities of Metals Resistivity Element OXIO ohm-cm. at 20C.

Aluminum 2.62 Antimony 39.0 Cadmium 7.5 Chromium 2.6 Copper 1.69

Gold 2.4

Indium Iron 10.0

Lead 21.9 Palladium 10.8

Silver 1.62 Tantalum 13.1 Thallium 18.1 Titanium 30 Zinc 6.0

Utilizing the known resistivities of the foregoing metals, the

length to width ratios of absorbing and reflecting dipoles can becalculated using equation (57) of parent application Ser. No. 378,836now U.S. Pat. No. 3,512,876, referred to hereinabove. These calculationsare summarized in Table 3 which sets forth the length to width ratiosfor absorbing and reflecting dipoles utilizing specified metals.

reflecting dipole is assumed to have a distributed resistance R of 8ohms. Values of 1.5 for n and 0.5 microns for )1 were used.

Thus, the properties of the metal dipoles can be determined beforehand,depending upon the length to width ratio and those sizes selected inaccordance with the particular property desired.

IIaving graded the sizes of the metal dipoles, these can then be used tomake a wide range of products. In this connection, reference is made toFIGS. 10 and 11 as illustrative of forming polarizer material in sheetform.

In FIG. 10, there is shown a supply roll 1 and a wind up roll 2 for athin film substrate or web 3 of plastic material, such as .celluloseacetate, cellulose acetate butyrate, acrylic, vinyl film or the like,having a thickness, for example of 0.1 to 1 mm. Film 3 passes overroller 4 where it is coated by a polymer solution 5 containing dipoles.The level 6 of the polymer solution is maintained by the feed 7, from alevel sensing device such as an inverted bottle (not shown). Evaporationof solvents from the coating is initially prevented by means of theshield 8. The dipole coating layer 9 shown in FIG. 11 remains liquid fora time sufficient to enable orientation of the dipole particles by anelectrical field 11. An electric field parallel to the surface of thecoating is maintained between a plurality of electrodes 12, 13, 14, 15,16, etc. in the vicinity of the coating 9. To minimize the effect of thevertical component of the electric field near the electrodes, cool airmay be provided in the areas and 21 by ducts 22 and 23 (FIG. 11). Thisdecreases the temperature, and increases the viscosity, of the coatinglayer 9 thereby preventing the dipoles from being disoriented by thevertical field component. In a similar manner, heated air may beprovided in the areas 25 and 26 by the ducts 27 and 28 to decrease theviscosity of the coating 9 where the component of the electric field ismost nearly parallel to the surface of the film. This enables thedipoles 10 to be aligned parallel to the surface of the coating 9. Thedipoles are fixed by passing the film 3 through the evaporation chamber30 (FIG. 10) which is provided with the input air duct 31 and the outputair duct 32 containing the evaporated solvent. The duct 31 may contain anumber of sections. Section 33 may be at a low temperature to freeze theparticles into alignment initially while evaporation is occurring.Section 34 may be at ambient temperature to continue the evaporation ofsolvent and section 35 may be at a higher temperature to evaporate theresidual solvent. The film emerging from section 35 over roll 36 is dry.

If an herapathite dipolar suspension is employed, the electric field 11is preferably AC field having a frequency of 10 to 100 kHz. at anelectric field intensity of l to 20 kv./cm. The best alignment isobtained at the greatest electric field intensity which is just underthe electric breakdown strength of air. Greater electric field strengthsmay be employed if the entire device is pressurized to severalatmospheres.

With metal dipoles in a nonionic fluid, DC or low frequency AC may beemployed, in the same electric field strength range.

The herapathite composition which may be employed contains submicronselected particles prepared for example as in Example I in the copendingapplication Ser. No. 378,836 previously noted.

Metal dipole suspension may, for example, be prepared as describedherein. In this connection, reference is made to a technical paperentitled Behavior of Unidirectionally Solidified Al-Al Ni Eutectic byLemkey, Hertzberg and Ford; Transactions of the Metallurgical Society ofAIME, Feb, 1965, Vol. 233, pages 334-341.

In this article, it is shown that at a growth velocity exceeding 3 cm.per hour, a spaced rod-like structure occurs initially. The spacingbetween the rods, and the rod diameter becomes smaller as the velocityincreases. The rod spacing is proportional to the inverse square root ofthe growth velocity. For example, extrapolation to 300 cm. per hourshows particle separation of 0.2 microns with and diameter of about300A.

The thermal gradient was between 25 and 37 C. per cm. A,

greater temperature gradient, which results in smaller dipole rods, maybe obtained by placing the eutectic in a small diameter tube, such as aquartz tube, having an inside diameter of 1 mm.

To achieve a dipole diameter of -300A, a thermal gradient of about 300C. per cm. may be used at a growth velocity of about 0.13 cm./sec. Afterthe rods are grown, the matrix is then dissolved away utilizing an acid,such as dilute hydrochloric acid. The particles may be further decreasedin size by washing them with a suitable acid, such as hydrochloric acid,until the optimum diameter and length has been ob tained. The dipolerods remaining undissolved are washed with water, and then with alcoholand acetone and dispersed in a solvent containing a polymer as describedabove.

The invention may be employed in the coating of lenses using a spincoating technique as follows with particular reference being made toFIG. 12

The object is to apply field of the order of 200 to 300 Kv./cm. acrossan air gap in which the coating is placed. The purpose of the device isto obtain maximum orientations and extremely large electrodichroicratios for coatings oriented in the plane of the surface of the lens.The effect is essentially electrostatic and the currents employed wouldgenerally be in the microampere range. The electric field is preferablyapplied across a distance not exceeding about 7 cms. on most lensapplications, an electric field of upwards of 1 million volts beingcontemplated for such a distance, the voltage being AC or DC. Since thegap normally required for a field of 1 million volts is about 33 cms,the electric breakdown strength must be increased by about 5 times. Thismay be accomplished by placing the element to be coated and aligned in apressure tank operating at about 5 times atmospheric pressure orapproximately 75 p.s.i.

In FIG. 12, a cylindric chamber 40 is provided with a cover 41 sealed byO-rings 42. A shaft 43 passes through cylindrical chamber 40 via asealed bearing 44, the shaft being inserted into the extending end oninsulated body 45. Slip rings 46 and 47 are connected through insulatedbushings 48 and 49, respectively, to terminals 50 and 51.

The bushings 48 and 49 should be large enough in diameter so that thepath length between the exposed conductors and the walls on the interioris greater than that which would afford a spark breakdown path under theestablished interior pressure conditions. Exterior atmospheric pressureconditions can be tolerated provided bushings 48 and 49 are extendedsufficiently outward to provide at least a 33 cm. total gap or they maybe alternatively immersed in an insulating oil bath 52. The dipole fluid53 is poured on lens 54 held within spin holder 54A and rotated alongwith electrodes 55 and 56 between which the intense electric field isestablished. Excess fluid is thrown off and the dipoles are oriented tovery nearly parallelism. Provision should be made for the evaporation ofthe solvent and for the provision of additional air to carry away theevaporated solvent. This may be done with an air source pipe 57 and anexit pipe 58 connected to a valve which controls the flow of air throughthe chamber.

The interior 59 of the chamber is desirably maintained at a pressure ofat least 75 p.s.i. before the application of the voltage. When theoperation is complete, the dipolar particles are aligned and evaporationhas occurred to solidify coating 53. The voltage is then turned off andthe rotation of shaft 43 stopped. The pressure within the chamber isreleased and the top 41 removed so that the coated lens can be taken outof the spin holder and another inserted.

A polarizing medium results after fluid layer shown in FIG 12 hassolidified (as by cooling if the fluid is a thermoplastic or a glass).For example, the dipoles may be metal needles, such as platinum, and themedium a low melting point low viscosity glass, such as solder glass Thedipole particles utilized in invention differ from those of prior artpolarizers, such as Polaroid J polarization which was an orientedherapathite suspension in cellulose acetate butyrate. The dipoles of thepresent invention are controlled in size and shape to close tolerances,whereas those of the prior art were of random size and shape.Consequently, polarizers produced in accordance with this invention haveno perceptible light scatter. Light polarizers according to this scatterwas a particularly serious disadvantage of prior art polarizers whichwere a result of the process of manufacturing, which caused largerparticles to be produced in situ.

As stated hereinbefore, semiconductors, as set forth, may be employed inthe preparation of such dipoles as described.

Preparation of Submicron Herapathite Crystals To produce submicronherapathite crystals in high concentration in a low viscosity suspendingfluid, which form an optically clear, non-scattering dipole particlesuspension of suitable electrodichroic ratio and sensitivity, thereacting solutions should be:

The iodine is dissolved in the normal propanol by heating and shaking.

Quinine Bisulphate 32.5

Methanol 67.5

For complete solution warm with agitation in a hot water This solutionis then warmed to 70 C. and pressure filtered at the same temperature toremove any small undissolved crystal which would act as nuclei forcrystallization.

Solutions Nos. 1 and 4 are then mixed in proportion and rapidly mixed ina container cooled by an acetone dry ice bath. The result is:

Before reaction After reaction Perercent cent Pts. Material SolidsSolids Solids No. l 9 Iodine 20.0 1.8 (Quinine Bisulph c) g 4.06 3.7 5.5lQS. 44.4

No. 91 (Nitrocellulose)... 7. 55 6.87 Nl 5 5;

While Solution No. 5 is being prepared, alkyl epoxy stearate(Celluflex-ZS), a high boiling solvent also known as a plasticizer iscooled in an ice bath to 0 C., and added in the following proportions tomake a paste containing the submicron herapathite particles insuspension:

Paste P cent Pts. Material Solids solids lodoquininesulphate... 4.24Sus- 13.0

pended SolutionNo.5 77 Nitrocellulose... ..30 16.3 Celluflex-23 23'Celluflex-23 23.0 solution 70.7

No. 6 is then mixed with a mechanical stirrer for about 10 minutes toinsure complete reaction and homogenity. After this, to remove thevolatile solvents, the suspension No. 6 is placed in a rotatingevacuator for about 2 hours and a paste is then obtained which issubstantially free from solvents except the plasticizer and which has aresistivity of at least 30 megohm-cm.

The analysis of the paste resulting from No. 6 after the volatiles havebeen removed is:

No. 9 may be used directly or be centrifuged to obtain a supernatentliquid for use in an electrodichroic system.

A herapathite suspension prepared in this manner is characterized byelongated submicron crystals of herapathite, which remain in suspensionwithout settling and which is suitable for use as a dipole particlesuspension in the practice of this invention.

Chemically, herapathite is quinine trisulphate dihydroiodide tetraiodidehexahydrate, the chemical name for 4C l-LO N 31-1 80 2H1 L, 61-1 0. Themolecular weight is 2,464.

Stoichiometrically herapathite contains approximately 25.8 percent ofiodine which is approximately a ratio of iodine to quinine bisulphate of1 [3.

However, I have found that the proportions can be varied from as throughA. This is apparently due to herapathite being a molecular compound or amixed crystal in which the proportion of the components may vary.

Moreoever, the HI in the compound is present in the proportion of twomoles of quinine to one of H1. The heating of the iodine solution No. 1usually sufi'ices to provide sufficient H1 as set forth in the aboveexample. The presence of H1 in stoichiometric quantities is required toform a stable crystalline compound. An additional quantity of H] may beadded to achieve the molar ratio set forth.

Generally, I have found the composition of Example A to be satisfactory,and this composition has been used in most of the tests.

As will be appreciated from the foregoing disclosure, the embodimentsprovided by the invention are many and varied. F or example, as oneembodiment, an article of manufacture is provided comprising a matrixhaving dispersed substantially uniformly at least at the surface thereofa plurality of dipoles selected from the group consisting ofelectrically conductive and semi-conductive material, such as metal orherapathite dipoles, the matrix being a medium capable of being in thefluid state during the initial dispersion of the dipoles whereby saiddipoles are capable of rotation to a desired preferred orientation uponthe application of a force field. Thus, the liquid state of the matrixmay be in the form of a solution that dries during the application ofthe force field, or the medium forming the matrix may be one which isconverted to the fluid state by the application of heat, but which iscapable of hardening during the application of a force field. The matrixmight be a coating applied to a surface, such as a curable plasticcoating; or it might be a coating applied to a transparent substrate,such as glass or a hard plastic.

The dipoles dispersed in the matrix may have an average length of aboutA/Zn 50 percent and an average diameter ranging up to about M n i 50percent, A being the wavelength of light and nthe index of refraction ofthe matrix medium. Depending on the wavelength of the particular lightstriking the surface, the dipoles may range in length from about 1,000Ato 10,000A.

The number of particles in a unit area of matrix medium may bedetermined simply by using the formula N 8n /A The interparticle spacingof the dipoles oriented in the plane of the matrix medium is generallyat least about the effective cross section of the dipole divided by itsaverage length, the effective cross section being determined by theformula: Effective cross section A /8n Another embodiment provided bythe invention is a composition of matter for a light controlling devicecomprising a transparent suspending medium and a plurality of dipoleparticles selected from the group consisting of conductive andsemi-conductive material suspended in the medium, the medium being onewhich is capable of being in a fluid state to enable the dipoles to berotated to a preferred orientation upon the application of anon-constant force field, the medium being then capable of beingsolidified at ambient temperatures during the application of the forcefield in order to fix the particular orientation of the dipoles desired.The type of dipole particles employed may be the same as those discussedherein before.

A further embodiment is an article of manufacture in the form of a solidtransparent layer of a medium having substantially uniformly dispersedtherethrough said dipole particles having a preferred orientationrelative to the plane of the transparent layer. The transparent layermay be a material selected from the group consisting of glass andplastic. By glass, is meant any transparent inorganic material capableof being worked into any desired shape, either by melting and shapingthe glass, or by forming a coating of the glass-like material onto atransparent substrate, such as with a solution which, upon drying,leaves a glass-like coating. Similarly, by plastic, is meant anytransparent organic material which is capable of being softened andshaped into any desired form or which can be employed as a solutionwhich leaves a coating after the solution has been evaporated from alayer deposited by the solution. In any event, it is any material of theforegoing type which is capable of having a fluid state during whichdipole particles dispersed through the fluid can be oriented by using anon-constant force field, which force field is maintained until it iscaused to harden or cure or form a permanent layer by drying.

As another embodiment, the invention provides a polarizer comprising asolid layer of transparent medium, such as glass or plastic, having asubstantially uniform dispersion therethrough of dipole particlesoriented in the plane of the layer, selected from the group consistingof electrically conductive and semi-conductive particles, the particlespreferably and advantageously having an average length of about A/Zn flOpercent and a diameter ranging up to about A/lOniSO percent. As statedabove, the dipole particles may advantageously be metallic and be spacedfrom each other in accordance with the preferred limitations statedhereinbefore.

The invention also provides a composite article of manufacturecomprising a substrate of a transparent material having a transparentoptical coating thereon, such as glass or plastic, and containing adispersion of dipole particles similarly as described herein.

The method embodiment of the invention for producing an article ofmanufacture of a transparent medium having preferred optical propertiesresides in providing the medium, e.g. glass or plastic, in the fluidstate containing a uniform dispersion of dipole particles selected fromthe group consisting of electrically conductive and semi-conductivematerial (eg metal dipoles), in forming a layer of the material in thefluid state, in subjecting the layer to the action of a force fieldwhereby to orient said dipoles in a predetermined direction, and inmaintaining the force field while allowing the layer to solidify. Thesolidification referred to may be the result of dry ing the fluid,allowing the fluid to harden or cure which, in the case of glass, wouldharden by cooling and the same is true for some plastics. However, theplastic might have a curing catalyst which causes hardening to takeplace while the force field is maintained.

The methods disclosed hereinabove may similarly be employed in producinga coated substrate of transparent material in which the coating may beof glass or plastic containing dipoles which is applied to the substratein a fluid state and the dipoles similarly oriented in the plane of thecoating using the non-constant force field.

A method which may be employed in efiecting the orientation of dipoleparticles in a transparent medium resides in providing the medium as alayer in the plastically deformable state (eg glass or plastic)containing a uniform dispersion of dipole particles, in physicallystretching the layer unidirectionally so as to orient the dipoles in theplane of the layer in the direction of stretch, and then allowing thestretched layer to congeal or harden to permanently fix the orientedpositions of the dipoles dispersed in the layer.

It will be understood that in polarizers made in accordance with thisinvention, the flakes (e.g. aluminum flakes) are oriented normal to thesurface and in parallel planes as shown in FIG. 8A. The orientationshown in FIG. 8A may be obtained by momentarily applying a pulsedelectric field along the Z-axis, followed immediately by a pulsedelectric field along the X-axis, whereby the particles are orientedalong the respective axes. The pulses are applied sufficiently rapidly,for example at a repetition rate of about 1,000 per second so that theflakes do not have a chance to disorient between successive pulses.Thus, the plane of substantially each of the flakes, when oriented, maybe parallel to two of the axes. For example, the plane of substantiallyeach of the oriented particles may be parallel to the plane of thelayer, or normal thereto.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.

What is claimed is:

1. A film, sheet or block of material comprising a matrix havingdispersed substantially uniformly therethrough a plurality ofelectro-optically responsive dipole particles selected from the groupconsisting of electrically conductive and semiconductive material anddichroic crystals, said matrix comprising a medium having separate fluidand solid states'and being in the fluid state during the initialorientation of the dipoles, and said dipoles being rotatable to apredetermined desired orientation upon the application of a force field.

2. The material of claim 1, wherein the dipoles are metallic.

3. The material of claim 1, wherein the dipoles have an average lengthof about A/Zn i 50 percent and an average diameter ranging up to aboutA/ lOn 50 percent, A being the wavelength of light and n the index ofrefraction of the matrix medium.

4. The material of claim 3, wherein the dipoles range in length fromabout 1,000A to 10,000A.

5. The material of claim 4, wherein the number of particles per unitarea is at least the reciprocal of the effective cross section perparticle.

6. A material in accordance with claim 1, wherein said materialcomprises a transparent optical coating on a substrate of transparentmaterial, said coating having said dipole particles oriented in theplane thereof, said dipole particles having an average length of aboutA/2n i 50 percent and an average diameter ranging up to about lOn 50%,where A is the wavelength of light and n" the index of refraction of thetransparent coating.

7. The material of claim 6, wherein the substrate and the coating areselected from the group consisting of glass and plastic.

8. The material of claim 6, wherein the dipole particles are metallic.

9. The material of claim 8, wherein the dipole particles have an averagelength of about 1,000A to 10,000A.

10. The material of claim 9, wherein the number of particles per unitarea is at least the reciprocal of the effective cross section perparticle.

11. A film, sheet, or block of matter for a light-controlling devicecomprising a transparent suspending medium and a plurality of dipoleparticles selected from the group consisting of conductive andsemi-conductive material, and dichroic crystals, suspended in themedium, said medium having separate fluid and solid states and being ina fluid state to enable the dipoles to be rotated to a predeterminedorientation upon the application of a force field, and said medium beingsolidified to permanently fix the rotational position of the dipoleparticles.

12. The matter of claim 11, wherein the transparent suspending medium isselected from the group consisting of glass and plastic. 7

13. The matter of claim 12, wherein the dipole particles have an averagelength of about )\/2n 1 50 percent, and an average diameter ranging upto about A/lOn i 50 percent, A being the wavelength of light and n theindex of refraction of the suspending medium.

Eli

14. The matter of claim 13, wherein the dipoles range from about 1,000Ato 10,000A in length.

15. The matter of claim M, wherein the dipole particles are metallic.

16. A film, sheet or block of material comprising a solid transparentlayer of a medium having substantially uniformly dispersed therethroughdipole particles selected from the group consisting of conductive andsemi-conductive material, and dichroic crystals, said particles having apreferred orientation relative to the plane of the transparent layer,and wherein the dipoles have an average length of about )t/Zn 50percent, and an average diameter ranging up to about )t/ 10n I 50percent, A being the wavelength of light and n" the index of refractionof the transparent medium.

17. The material of claim 16, wherein the dipoles are metallic and havean average length falling within the range of about 1,000A to 10,000A.

18. The material of claim 16, wherein the umber of particles per unitarea is at least the reciprocal of the effective cross section perparticle.

19. A polarizer comprising a solid layer of transparent medium having asubstantially uniform dispersion therethrough of dipole particlesoriented in the plane of said layer selected from the group consistingof electrically conductive and semiconductive particles, and dichroiccrystals, said dipole particles having an average length of about t/2n i50 percent and an average diameter ranging up to about k/lOn 1 50percent, where A is the wavelength of light and n" the index ofrefraction of the transparent material.

20. The polarizer of claim 19, wherein the transparent material isselected from the group consisting of glass and plastic.

21. The polarizer of claim 19, wherein the dipole particles aremetallic.

22. The polarizer of claim 21, wherein the dipole particles have anaverage length of about 1,000A to 10,000A.

23. The polarizer of claim 22, wherein the number of particles per unitarea is at least the reciprocal of the effective cross section perparticle.

24. A polarizer comprising a layer of transparent material containing auniform dispersion of flake particles selected from the group consistingof electrically conductive and semiconductive material, and dichroiccrystals, the plane of the layer being referenced to a coordinate systemhaving three mutually perpendicular axes described as the X-, Y- and Z-axes, and the flakes being oriented such that the plane of substantiallyeach of the flakes is parallel to a plane formed by two of said axes.

25. The polarizer of claim 24, wherein the flakes are substantiallynormal to the plane of the layer.

26. The polarizer of claim 25, wherein the flakes are aluminum.

2. The material of claim 1, wherein the dipoles are metallic.
 3. Thematerial of claim 1, wherein the dipoles have an average length of aboutlambda /2n + or - 50 percent and an average diameter ranging up to aboutlambda /10n + or - 50 percent, lambda being the wavelength of light and''''n'''' the index of refraction of the matrix medium.
 4. The materialof claim 3, wherein the dipoles range in length from about 1,000A to10,000A.
 5. The material of claim 4, wherein the number of particles perunit area is at least the reciprocal of the effective cross section perparticle.
 6. A material in accordance with claim 1, wherein saidmaterial comprises a transparent optical coating on a substrate oftransparent material, said coating having said dipole particles orientedin the plane thereof, said dipole particles having an average length ofabout lambda /2n + or - 50 percent and an average diameter ranging up toabout lambda /10n + or - 50%, where lambda is the wavelength of lightand ''''n'''' the index of refraction of the transparent coating.
 7. Thematerial of claim 6, wherein the substrate and the coating are selectedfrom the group consisting of glass and plastic.
 8. The material of claim6, wherein the dipole particles are metallic.
 9. The material of claim8, wherein the dipole particles have an average length of about 1,000Ato 10,000A.
 10. The material of claim 9, wherein the number of particlesper unit area is at least the reciprocal of the effective cross sectionper particle.
 11. A film, sheet, or block of matter for alight-controlling device comprising a transparent suspending medium anda plurality of dipole particles selected from the group consisting ofconductive and semi-conductive material, and dichroic crystals,suspended in the medium, said medium having separate fluid and solidstates and being in a fluid state to enable the dipoles to be rotated toa predetermined orientation upon the application of a force field, andsaid medium being solidified to permanently fix the rotational positionoF the dipole particles.
 12. The matter of claim 11, wherein thetransparent suspending medium is selected from the group consisting ofglass and plastic.
 13. The matter of claim 12, wherein the dipoleparticles have an average length of about lambda /2n + or - 50 percent,and an average diameter ranging up to about lambda /10n + or - 50percent, lambda being the wavelength of light and ''''n'''' the index ofrefraction of the suspending medium.
 14. The matter of claim 13, whereinthe dipoles range from about 1,000A to 10,000A in length.
 15. The matterof claim 14, wherein the dipole particles are metallic.
 16. A film,sheet or block of material comprising a solid transparent layer of amedium having substantially uniformly dispersed therethrough dipoleparticles selected from the group consisting of conductive andsemi-conductive material, and dichroic crystals, said particles having apreferred orientation relative to the plane of the transparent layer,and wherein the dipoles have an average length of about lambda /2n +or - 50 percent, and an average diameter ranging up to about lambda/10n + or - 50 percent, lambda being the wavelength of light and''''n'''' the index of refraction of the transparent medium.
 17. Thematerial of claim 16, wherein the dipoles are metallic and have anaverage length falling within the range of about 1, 000A to 10,000A. 18.The material of claim 16, wherein the umber of particles per unit areais at least the reciprocal of the effective cross section per particle.19. A polarizer comprising a solid layer of transparent medium having asubstantially uniform dispersion therethrough of dipole particlesoriented in the plane of said layer selected from the group consistingof electrically conductive and semi-conductive particles, and dichroiccrystals, said dipole particles having an average length of about lambda/2n + or - 50 percent and an average diameter ranging up to about lambda/10n + or - 50 percent, where lambda is the wavelength of light and''''n'''' the index of refraction of the transparent material.
 20. Thepolarizer of claim 19, wherein the transparent material is selected fromthe group consisting of glass and plastic.
 21. The polarizer of claim19, wherein the dipole particles are metallic.
 22. The polarizer ofclaim 21, wherein the dipole particles have an average length of about1,000A to 10,000A.
 23. The polarizer of claim 22, wherein the number ofparticles per unit area is at least the reciprocal of the effectivecross section per particle.
 24. A polarizer comprising a layer oftransparent material containing a uniform dispersion of flake particlesselected from the group consisting of electrically conductive andsemi-conductive material, and dichroic crystals, the plane of the layerbeing referenced to a coordinate system having three mutuallyperpendicular axes described as the X-, Y- and Z-axes, and the flakesbeing oriented such that the plane of substantially each of the flakesis parallel to a plane formed by two of said axes.
 25. The polarizer ofclaim 24, wherein the flakes are substantially normal to the plane ofthe layer.
 26. The polarizer of claim 25, wherein the flakes arealuminum.